It is known that the introduction of charge material in end-fired furnaces is significantly more difficult and less satisfactory than in cross-burner furnaces. In the end-fired furnaces, so-called doghouses are provided on one side or on both sides of the furnace longitudinal axis; the charge material is placed into the doghouses from above and is pushed in the direction of the melting tank. These doghouses act as pre-sintering zones. If the doghouses are made too small, the not yet pre-melted batch is exposed at the surface to the flame flowing above it at a high speed. This causes a high degree of dust to develop in the melting tank, and the dust deposits on the side walls and on the tank cover, and, together with the refractory material, enters into low-melting compounds. This is known in connection with the corrosion of refractory materials. In addition, parts of the dust are carried into the regenerative chambers. There as well, the dust reacts with the refractory material and results in corrosion. In addition, the dust can also collect on the grating in the regenerative chambers and can reduce the efficiency of the air pre-heating. This type of dust contamination is even more pronounced in particular with the use of pre-heated batch material, with the named consequences.
In his book, “Glasschmelzöfen, Konstruktion und Betriebsverhalten [Glass melting furnaces, construction and operating performance]”, Springer-Verlag, Berlin, Heidelberg, New York, Tokyo, 1984, page 154, Dr. Wolfgang von Trier describes this problem and suggests, inter alia, to correspondingly enlarge the doghouse. The fact that up to today this has not been realized is clearly due to the fear that in a larger doghouse the glass would freeze in, i.e. would become too cold. The known front parts have therefore deliberately continued to be kept small.
The problem is thus that the introduced raw material mixture has a too-short dwell time in the pre-sintered zone, i.e. the doghouse. It is known that for a mixture of raw materials suitable for production of a glass melt a finite period of time is required in order to sinter the surface as a pile in an environment having a temperature of greater than 1000° C. This surface sintering of the supplied batch prevents the danger of the above-described dust contamination.
The dwell time of the material in the doghouse can be determined from the raw material bulk, the surface of the doghouse, the density of the pile, and the charging quantity per time unit. Here, the mass flow per hour conveyed through the doghouse into the melt installation is decisive. This defines the so-called K factor. This is generally known as a measure of the specific melting performance of a glass melting furnace. The use of the K factor in connection with the doghouse is not known.
Independently of the above-described damaging dust contamination, in short doghouses the charge material also loses thermal energy to the atmosphere, and this energy is lost to the melting process.